EP1386865B1 - Method for providing sheets in a printing machine - Google Patents

Abstract

The sheet setting up process is for a press in which the sheets are taken along a transporting path (1a) from one or more feed units (2) on a transporting belt (1b) running through a printing unit (4). The starting time point for feeding in a sheet from one or more feed units is selected on the basis of the type of material of which the sheet is made.

Description

The invention relates to a method for providing sheets for single-sided or double-sided printing (simplex, duplex, double-sided printing) in a digital printing machine, preferably in an electrophotographic printing machine, the sheets being a transport path from one or more feed units (feeder). be supplied and in the course of the transport path to a conveyor belt (web), which passes through a printing unit, with the least possible space between successive sheets passed.

From the DE-A-100 23 828 a method of the above-mentioned type is known.

From the EP-A-0798607 a document feeder is known with a control device for controlling the timing.

From the US Pat. No. 6,076,821 a sheet feeder is known in which a Zufuhrungzeit a previous sheet is determined.

The EP 0 414 623 describes a device for controlling the gap width between leaves.

From the " Patent Abstracts of Japan vol. 009, no. 219 (M-410), September 6, 1985 (1985-09-06 ) JP 60 077051 A (Fuji Xerox KK), May 1, 1985 ( 1985-05-01 ) discloses a method for providing paper sheets, wherein the time to reach a position on a transport path is measured.

In an electrophotographic printing machine, which is to be explained in more detail, but without limitation to such a type of printing machine, to be printed sheets from one or more investors a paper path, or more generally a transport path for printing material of any kind supplied. The presence of several rer investors or feed units allows the provision of substrate in particular different formats, weights, materials or the like. This is particularly advantageous in a digital printing press, because there is already reimaged for each individual page to be printed anyway and therefore also mixed print jobs can be processed easily, for example, where such a single print job consists of the pages of a booklet, the immediate successively the printing unit and optionally also a finishing be supplied, for example, the front and the rear cover sheet could have a heavier paper and subsequent pages lighter paper and possibly even plastic films could be printed with diagrams or the like. These different substrates would be provided in different feed units and would feed, in a preselected sequence, to some extent intermittently as arcs in the transport path.

In this case, a first transport path section, which begins at the feed units, for example, consist of circumferentially driven clamping belt, between which the sheets are transported. Thereafter, the sheets could be transferred to a circulating driven conveyor belt and placed and adhere there by electrostatic forces. This conveyor belt is usually a transparent plastic belt and leads through a printing unit, which can of course consist of a color printing of several printing units. In electrophotographic printing, a latent toner image per color separation is transferred to the sheet. Thereafter, the sheet is further transported to a fixing unit, in which the toner image is connected to the printing material, in particular melted and cooled. For transport into and through the fixing unit, a change of the transport member could again take place in the transport path. Only sheets to be printed on one side are then transported further or output in a delivery arm. Both sides to be printed sheets are returned and turned over a transport path loop after fixing for further printing in front of the printing unit. The return transport and the turn can for example be done simultaneously, in turn, that for this transport path section clamping belts are used, the take a certain helical course and thereby rotate the sheets around their longitudinal axis extending in the transport direction by 180 °.

In particular, the leading through the printing unit conveyor belt, which is often referred to in the electrophotography as web, should be covered with sheets to be printed with the smallest possible spaces between the sheets to have the highest possible throughput per time, so to ensure the highest possible printing performance , On the other hand, minimum distances between successive sheets must be respected. This applies both in the one-sided printing of the front sides of the sheets, as well as the two-sided printing for the printing of the front sides and the backs of the sheets in reverse printing.

In order to achieve the most optimal or coordinated use of the web, the web is mentally or control technology in areas that can be referred to as frames or frames, divided into each of which a sheet, taking into account the popular formats, placed precisely for printing shall be. In this case, an area of the web is left out, in which there is a transverse seam, by means of which the ends of the web are connected to form the web as a closed loop. This seam is also commonly used for convenience as a marker and registered by a sensor to control the orbital position of the web and to have a reference point. This seam must therefore not be covered by a bow. Of course, other markings would also be considered, especially those that are only attached to the edge of the web.

So that these frames on the conveyor belt, even when printing on both sides after a return transport of the sheets, are again encountered exactly for a transfer of the sheets, the running time of the sheets circulating over the return after the printing of the first page and the running time of the web should be in an integer ratio stand. However, problems can occur in all that by the sheet travel times are influenced within the considered printing press of a variety of parameters. For example, paper weight and paper length have been the dominant paper influences. Likewise, machine-specific parameters such as the exact transport path lengths, roll diameters and motor speeds contribute to this.

This behavior is the cause of various problems associated with the runtime of the press (e.g., image quality, insufficient paper spacing). This is particularly noticeable when printing mixed paper. For example, thick (heavy) leaves have shorter durations than thin leaves. As a result, during the passage through the machine, the distance between two successive sheets can be significantly reduced (the fast, thick catching up), which then leads to an interruption of the printing function due to insufficient blade spacing and thus to a significant loss of performance of the machine. Also bows may possibly come to rest on the web-seam and thus be the trigger for image errors.

The invention is therefore based on the object to show a method of the type mentioned, which is suitable to provide the sheets improved.

This object is achieved in method view by the features specified in claim 1, advantageous developments are given in the dependent claims.

It is advantageous that the sheets depending on their type, ie in particular length and / or weight, started at different times, that is, given from the respective feed unit in the transport path to be expected in this way on the transport, self-adjusting incorrect positions Bows, in particular also to each other, from the outset so to compensate, so to be liable with an opposite error that sets the desired position during transport.

In order to be able to carry out such a precontrol in a targeted manner quantitatively, it is provided that information for selecting the starting time is obtained beforehand by at least one test run with at least one type of printing material, preferably by trial runs of different types and with the preparation of a corresponding empirical table, for example in the form of a look-up tables.

In the feedforward control, the type can be taken into account directly. However, it can also be assumed that different types are stored in different feed units. As with another solution provided, a start time for feeding from one of the feed units can be selected in each case relative to the relevant feed unit.

The former solution is particularly advantageous even in the presence of only a single feed unit. The second-mentioned solution has the advantage that, regardless of the types stored, also path length tolerances can be compensated during transport from different feed units by being compensated in advance by choosing appropriate start times. Of course, even with a single feed unit, path tolerances can occur between different machines, for example due to structural inequalities or changes due to maintenance work, so that an exact setting can not be made ex works and, according to the invention, this can also be taken into account when choosing a start time.

In general, it is desirable to be able to correct misstatements or erroneous runtimes, without the cause of it would have to be clarified or taken into account, especially as in informative test runs no accurate predictions for each additional sheet of the same type are possible and statistical fluctuations are present. The pre-signed pilot controls can therefore only relatively flat and coarse, based for example on the method of least squares, performed.

In order to enable a more accurate, reliable and more individual correction, the solution of the problem according to the invention therefore provides that with at least one sensor (S2) the arrival time of at least one arc is registered at the location of the transport path marked by the sensor (S2) and that by means of said arrival time of said registered sheet, a starting time for feeding at least one next sheet which is still in the same feeding unit from which the registered sheet originated is selected or corrected from said feeding unit into the transport path.

In this solution according to the invention, it is thus advantageously again checked which arrival time an arc actually has at a location determined by the sensor, this time of arrival, of course, not being absolute, but being seen primarily relative, preferably with respect to the then given position of by the printing unit leading conveyor belt, which could be detected with a mark of the conveyor belt and a second sensor.

The sheet thus registered can be corrected in terms of its position only by an aftertreatment, which should be left out of consideration in the context of the present invention, except for a possible return to the printing of its back, as will be discussed in more detail later. In the context of the present invention, the registration of the incoming sheet by the sensor is intended primarily to use this information obtained for at least one sheet is still in the same feed unit from which the registered sheet has come and the next in the Transport path should be given. For this arc can be selected from the sensor information an improved start time, for example by determining such a start time or by appropriate correction of an existing, for example, type-based, flat start time, to achieve that this newly corrected bow arrives more precisely than the previously registered Bow.

For such an improvement, a time difference is determined with the information of the sensor which reflects an arrival error, namely in that the time deviation between the registered arrival time (actual time) of the registered sheet and the expected time of arrival calculated from its starting time (nominal time). Timing) and used as a correction value for the correction for the start time for feeding at least one next sheet, which is still in the same feed unit from which also the registered sheet comes from this feed unit is used in the transport path.

In particular, according to the invention, the sheets which originate from the same feed unit are always controlled relative to one another, while sheets from different feed stations, or at least not by the control, are not correlated with one another, even if such sheets are used jointly and in terms of the overall result to be achieved successively in the transport path for a mixed print job.

If only the registered sheet from a particular feed unit and no sheet follows it from the same feed unit already in the transport path section between the sensor and the feed unit, the evaluation of the sensor for this sheet alone is taken to start at least the next sheet from the same feed unit , Then, but not the entire time difference of the only registered sheet for the correction of the arc to be started will be taken, because this does not have to be representative of all arcs. As a precaution, only a proportion of the measured time error is taken into account for the start time of the sheet to be started, for example 80%, in order not to overdrive. Namely, the algorithm described here should preferably be taken as a start-up algorithm by which a correction of the sheet travel when starting the printing machine is to take place as quickly as possible, although as roughly as possible, and as asymmetrically as possible to the desired value, without control oscillations.

This also applies if several sheets originate from the same feed unit when starting up. However, the measured time errors can then be averaged over existing sheets, which leads to a more reliable correction of the starting times of the sheets still to be launched, namely according to the invention in that, if several originating from the same feed unit sheets in the transport path section between the feed unit and the location of the sensor (S2) at the time of registration of the arrival time of the first arriving at the sensor sheet of these sheets, for this first registered sheet and for subsequent path in the transport path section from the same feed unit respectively the time difference between the registered arrival time (actual time ) of this registered sheet and the estimated time of arrival (DESIRED) calculated from its start time, and each time as a correction value for the correction for the starting time for feeding at least one next sheet, d is still in the same feed unit from which also the registered sheet originates, is used from this feed unit into the transport path, but each divided by the number n ₁ of the sheets located in the transport path section from this same feed unit.

However, in order to maintain its speed in the described approach algorithm, if the number of sheets in the transport path section from the same feed unit is too large, the time difference of all these sheets is not taken into account for correction, but rather it is preferred that the number n _{1 be} in the transport path section Arcs from this feed unit are taken as dividers only if they do not exceed a fixed maximum number n ₂ , which is an element of the set of natural numbers, and otherwise this maximum number n _{2 is} taken as a divisor instead of the actual number n ₁ .

For example, n ₂ could be set equal to 3.

In this case, it is then preferably provided that only those sequence sheets lying in the transport path section which follow the first registered sheet are used to calculate correction values whose serial number, counted from the first registered sheet, is less than or equal to the set maximum number n ₂ during the further follow-on sheets with a sequence number greater than n ₂ and less than or equal to n _{1 are} disregarded for a correction of new sheets to be fed from the feed unit.

If the printing press has started up and the paper run is calibrated by the described algorithm, in the subsequent operation of the printing press, preference is given to a dynamic operating algorithm as an operating algorithm, which is characterized in that the time deviation between the registered arrival time (actual time) of each at the sensor (S2) incoming arc and the expected time of arrival calculated from its start time and determined as a correction value for the correction for the start time or as a correction of the already prepared for the correction of this starting time correction value of the next arc, which is still in the same feed unit from which also the registered sheet originates, is used for the supply from this feed unit in the transport path provided in sheet, but each divided by the number n ₁ in the transport path section together with the respective re Registered sheet straight sheets from this same feed unit.

This change-over in the operating algorithm is preferably carried out after the unaccounted for correction arcs of the numbers n ₂ + 1 to n ₁ of the Anfahralgorithmus have passed the sensor.

In this operating algorithm, too, however, overmodulation and control oscillations are to be avoided, which is preferably achieved by dividing, instead of the number n _1, a set value n ₃ , which is an element from the set of natural numbers, if n _{1 is} less than or equal to n ₃ is.

For example, n ₃ could be set equal to 5.

Since the transport path of a sheet to be printed on both sides is different from that of a sheet to be printed on only one side, in particular the return path is added to the transport path is provided for both sides to be printed sheets according to the invention with advantage that a start time for supplying a sheet, for a double-sided Printing is provided, is selected differently from one or the feed unit than for a sheet from the same feed unit, which is provided only for a one-sided printing.

The runtime errors that are likely to occur due to the return can also be precompensated in this way according to the invention.

A type of printing material can also be taken into account in this compensation.

Should nevertheless be determined with the sensor by registering the arrival times of these sheets to be printed on both sides, that despite the precompensation a runtime error will remain, so it should still be compensated according to the invention in the return path. For this purpose, a development of the invention provides that a group of double-sided sheets to be printed after printing their respective first pages to print their respective second pages in the transport direction before the printing unit transported back and turned and gets granted in this way a speed or a speed change, which is suitable for correcting or at least reducing a misplacement of these sheets in relation to a desired position, at least in the group means.

In this measure according to the invention, the whole group, which may also be referred to as a block, of sheets in the return path into consideration. To is to be considered that unilaterally to be printed sheets can be promoted quasi-continuous by the printing unit, because the transport has, so to speak, an open end, while the limited capacity of the return path back printing can only be done in groups or in blocks. It must, as already explained above, the circulation through the return path with the circulation of the conveyor belt (web) be tuned in integer ratio. For this purpose, a group-wise consideration of the arcs is appropriate and a time correction should be carried out mainly based on the mean error of the group, under certain circumstances even regardless of whether or not a start time correction of the individual sheets has taken place.

Incidentally, the start-up algorithm and the operating algorithm can in principle also be regarded as independent of whether or not the start time of a sheet has also been corrected in this regard for a planned two-sided printing, because the actual starting time can be taken into account in these other algorithms. The system can "know" the respective actual start times and the number of completed starts at any time and take this into account when evaluating the sensor.

Especially in the return path, it may thus be provided to accelerate or slow down bends to their correction. Of course, this is also conceivable in principle in other transport sections, in particular also in addition to or as an alternative to a change in the start time of a sheet, but a change of the starting time without complication and additional burden on the mechanics in a simpler manner by software is possible. In fact, it should be noted at this point once again that of course the right time of arrival or the arc distance is the goal, no matter how it is ultimately achieved.

In order to set the critical return for sheets to be printed on both sides correctly with respect to a minimum distance, in particular to avoid jamming of the printing material, it can be provided that the for the Return Transport provided transport path for a test run is equipped with at least one arc less than it is provided for testing for subsequent runs.

A device of the type mentioned, is characterized in that at least one sensor (S2) is provided for registering the arrival time of at least one arc at the by the sensor (S2) excellent location of the transport path and that the sensor (S2) with a control unit is operatively connected by means of the registered arrival time point of the registered sheet a start time and / or the transport speed for feeding at least one next sheet, which is still in the same feed unit from which also the registered sheet comes from this feeding unit into the transport path and / or pretends or corrects along the transport path.

It should be pointed out once again that the aforementioned values n ₁ , n ₂ and n _{3 can} ultimately be adapted to the mechanical properties, in particular the available path lengths, the printing machine, the desired machine behavior and / or the desired rate of change of the corrections ,

An embodiment of a transport path through a printing press, to which the invention is not limited in scope, is shown schematically in the single figure of the drawing and only by way of example in a side view.

The transport path 1 starts at a feed unit or a plurality of feed units, which together are indicated schematically only as block 2. From there, sheets are fed in the transport direction according to the arrows 3 to the transport path, that is, in particular started at a specific start time.

A first transport path section 1 a ends in front of a circulating conveyor belt which forms a second transport path section 1 b and to which the sheets are transferred in order to pass through a printing unit with four color printing units 4 in this case.

Approximately in the transfer area of the first to the second transport path section 1 a, 1 b, two sensors S1 and S2 are arranged. The sensor S1 detects a transverse seam of the conveyor belt 1 b as a mark of this conveyor belt. The sensor S2 detects the arrival of a bow in its area. Both sensors are in connection with a control device 5, which in turn according to the invention acts on the feed unit or units 2, preferably from the information from the sensor S2, taking into account the information from the sensor S1, a start time for at least one next from the feed unit. 2 determined or corrected to be started bow.

After the passage of the sheets past the printing units 4 and a printing of their front pages, the sheets are after transition to a third transport path section 1 c of a fixing device with a fixing roller 6 and a counter-pressure roller 7 supplied.

After fixing the sheets reach a path switch 8. Only one-sided to be printed sheets are transported in the direction of arrow 9 to a boom no longer shown. Both sides to be printed sheets are directed in the direction of arrow 10 in a return path 1 d. This transports the sheets back into the area of the sensors S1 and S2 in front of the printing unit. It comprises a turning device 11, with which the sheets are rotated about their longitudinal axes by 180 °, as indicated by an arrow 12.

An empty strand of the endless conveyor belt 1 b moves in the direction of the arrows 13.

Claims (9)

1. Method for providing sheets for simplex-printing or duplex-printing in a digital printing machine,
   wherein the sheets are fed to a transport path from one feeder unit or from several feeder units and are transferred along the transport path to a transport belt with the smallest possible space between successive sheets, said transport belt passing through a printing unit,
   wherein at least one sensor (S2) is used to register the arrival point in time of at least one sheet at the location of the transport path identified by the sensor (S2) and that, by means of the arrival point in time of said registered sheet, a starting point in time for feeding at least one subsequent sheet from said feeder unit into the transport path, said sheet still being in the same feeder unit from which the registered sheet also originates, is selected or corrected,
   characterized in that
   the time difference between the registered arrival time (ACTUAL time) of said registered sheet and the expected arrival time (SET time) computed from the starting point in time of said registered sheet is determined and used as a correction value for the correction of the starting point in time for feeding at least one subsequent sheet into the transport path, said sheet still being in the same feeder unit from which the registered sheet also originates, whereby, if several sheets coming from the same feeder unit are present in the transport path section between the feeder unit and the location of the sensor (S2) at the time of registration of the arrival time of the first sheet of said sheets arriving at the sensor, for said first registered sheet and for the subsequent sheets coming from the same feeder unit and being present in said transport path section, the time difference between the registered arrival time (ACTUAL time) of said registered sheet and the expected arrival time (SET time) computed from the starting point in time of said registered sheet is determined for each sheet and used as the correction value for the correction of the starting point in time for feeding at least one subsequent sheet from said feeder unit into the transport path, said sheet still being in the same feeder unit from which the registered sheet also originates, however, each correction value is divided by the number n₁ of the sheets in the transport path section, said sheets coming from the same feeder unit.
2. Method as in Claim 1, characterized in that the number n₁ of sheets from said feeder unit present in the transport path section is only used as the divisor if said number does not exceed a fixed maximum number n₂, said fixed maximum number being an element of the set of natural numbers, and that, otherwise, said maximum number n₂ is used as the divisor instead of the actual number n₁.
3. Method as in Claim 2, characterized in that in that only those subsequent sheets following the first registered sheet and being present in the transport path section are used for the computation of correction values, whose consecutive number, counted as of the first registered sheet, is less than or equal to the fixed maximum number n₂, while the additional subsequent sheets having a consecutive number greater than n₂ and smaller than or equal to n₁ are not considered in the correction of sheets that are to be newly fed from the feeder unit.
4. Method as in Claim 2, characterized in that in that the number n₁ is defined as the number of sheets that are from the same feeder unit as the registered sheet and are in the transport path section at the same time as said registered sheet.
5. Method as in Claims 2 through 4, characterized in that in that the described algorithm is only used as the start-up algorithm at the start-up of the printing machine.
6. Method as in one or more of the previous Claims, characterized in that a starting point in time for feeding a sheet intended for duplex-printing from a feeder unit or from the feeder unit is selected differently from that for a sheet intended for simplex-printing from the same feeder unit.
7. Method as in Claim 6, characterized in that the difference between the starting point in time for a sheet that is to be duplex-printed and for a sheet that is to be simplex-printed is selected in relation to the type of printing material of which said sheet consists.
8. Method as in Claim 6 or 7, characterized in that a group of sheets that are to be duplex-printed after their respective first sides have been printed, are transported back in transport direction in front of the printing unit and are turned over for printing their respective second sides, said group of sheets thus being subjected to a velocity or to a velocity change that is suitable to correct or at least reduce, at least in the group mean, any incorrect positioning of said sheets relative to a SET position.
9. Method as in Claim 8, characterized in that, for a test run, the transport path intended for the return transport is loaded with at least one less sheet than is intended for the runs following testing.

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